Mitochondrially targeted p53 has tumor suppressor activities in vivo.

Complex proapoptotic functions are essential for the tumor suppressor activity of p53. We recently described a novel transcription-independent mechanism that involves a rapid proapoptotic action of p53 at the mitochondria and executes the shortest known circuitry of p53 death signaling. Here, we examine if this p53-dependent mitochondrial program could be exploited for tumor suppression in vivo. To test this, we engage Emu-Myc transgenic mice, a well-established model of p53-dependent lymphomagenesis. We show that exclusive delivery of p53 to the outer mitochondrial membrane confers a significant growth disadvantage on Emu-Myc-transformed B-cells of p53-deficient or alternate reading frame-deficient genotypes, resulting in efficient induction of apoptosis and impinged proliferation. Conversely, normal cells from thymus, spleen, and bone marrow showed poor infectivity with these viruses. This proof-of-principle experiment shows that exclusive reliance on the direct mitochondrial program exerts a significant tumor suppressor activity in vivo. Our in vivo data on the direct mitochondrial apoptotic p53 program lays the groundwork to further investigate its efficacy and safety and to address its possible therapeutic value in the future.